Along Party Lines

The vote on advancing the measure was along party lines, with two exceptions. Republican Susan Collins of Maine voted to move the bill forward and Democrat Mark Pryor of Arkansas voted against it. Four senators -- one Democrat, two Republicans and independent Joseph Lieberman of Connecticut -- were absent.

"There is no disputing that the wealthy should pay their fair share in taxes," Pryor said in a statement. "This inequity should be fixed as part of broad tax reform, not as a political ploy meant to score points."

The bill, sponsored by Senator Sheldon Whitehouse of Rhode Island, would impose a minimum tax rate of 30 percent for households with adjusted gross incomes of at least $2 million. Those with at least $1 million in income would pay the tax on a sliding scale to bring their rates closer to 30 percent.

The calculation includes payroll taxes as well as a 3.8 percent tax on unearned income set to take effect for high earners next year. Taxpayers would still be able to deduct charitable contributions.

High-Income Households

The tax would affect a minority of high-income households that manage to pay relatively low rates because of deductions and preferential tax rates on investment income. The bill is named for billionaire investor Warren Buffett, who says he pays a lower tax rate than his secretary.

The bill would raise $47 billion over the next decade, assuming that existing income tax cuts are allowed to expire as scheduled at the end of 2012. If those tax cuts were extended, the measure would raise about $162 billion, according to Whitehouse's office.

By 2015, the plan would impose higher taxes for 217,000 households, according to the Tax Policy Center, a nonpartisan research group in Washington.

According to administration data, the median effective tax rate for the middle 20 percent of U.S. taxpayers is 13.3 percent, including income, payroll and corporate taxes. For the top 1 percent of taxpayers, the rate is 29.6 percent, according to the 2012 Economic Report of the President. Still, 10 percent of high-income households have tax rates of 8.7 percent or less.

Equal Outcomes